Electrostatic writing tube



March 1959 H. c. BORDEN ETAL 2,879,422

ELECTROSTAT'IC WRITING TUBE Filed Feb. 7, 195a .a/arcre/r me/m/a Mia/0M can/fem S/GA/AL 00 965 ff/ 6.2, I

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United States Patent 2,879,422 ELECTROSTATIC WRITING TUBE Howard C. Borden, Atherton, and Robert W. Crews, Palo Alto, Calif., assignors to A. B. Dick Company Application February 7, 1958, Serial No. 713,831 5 Claims. (Cl. 313-89) This invention relates to electrostatic printing tubes, and more particularly to improvements therein.

In an application for Electrostatic Printing System, by John L. Tregay, filed May 10, 1957, Serial No. 658,275, and assigned to a common assignee, there is described an improved electrostatic printing tube which has as its target a wire array consisting of small-diameter, short, closely spaced, parallel and mutually insulated w rev segments which have one of their ends extending through the target wall to the outside of the tube. A conductive plane at anode potential, which can thus be termed an external anode, is positioned opposite the Wire ends which are outside the tube, and a dielectric writing medium is passed between the external anode plane and the wire ends. Means are provided for sweeping the electron beam generated in the tube across the wires and maintaining the beam turned off, except when it traverses selected ones of the wires. These wires then charge up toward the cathode potential. When the potential of any wire reaches a critical value with respect to the external anode, a discharge takes place between that wire and the plane. If the writing medium is present, it is at anode potential and the discharge results in a spot of charge under the wire and on the dielectric writing material. Means are provided for repetitively sweeping the electron beam across the wires as well as controlling its intensity so that, as the dielectric writing medium is moved, charges are deposited thereon which, upon subsequent development, produce visible characters corresponding to the ones dictated by the deflection and intensity-control signals.

With the target configuration described, the wire-t0- wire capacity is high, whereas the wire-to-anode capacity is low. As a result, when the electron beam strikes a given wire and causes it to charge toward cathode potential, the adjacent wire, and to a lesser degree, all succeeding wires, also charge towards cathode potential because of the coupling capacity between them. This effect can result in loss of definition.

An object of this invention is to minimize detrimental wire-to-wire capacity in an electrostatic writing tube.

Another object of this invention is to provide a novel and improved target arrangement for an electrostatic writing tube.

Still another object of the present invention is to provide an improved electrostatic printing tube.

Yet another object of the present invention is to provide an electrostatic printing tube which has better definition than was obtainable heretofore.

These and other objects of the invention are achieved by providing an electrostatic printing tube having each reading wire separately supported in a minimal length of dielectric and by making the reading wire itself as short as possible.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

Figure 1 is a cross section of an electrostatic tube including an improved target in accordance with this invention;

Figure 2 is an enlarged cross section of a means for supporting a writing wire in accordance with this invention as shown in Figure 1; and

Figure 3 is a cross section of another embodiment of an improved means for supporting a writing wire in accordance with this invention.

Reference is now made to Figure l, where there may be seen a cross-sectional view of an electrostatic writing tube with an improved target in accordance with this invention. The electrostatic writing tube is a conventional cathode-ray tube, except for its target.

Thus, it includes an evacuated envelope 10, which has therein a cathode 12, a control electrode 14, an anode or accelerating electrode 16, a focus coil 18, and a deflection coil 20. The cathode 12 is connected to a negative point of potential in the operating-potential supply 22. Signals are applied to the intensity-control grid from a signal source 24. Deflection signals are applied to the deflection coil from a deflection-signal source 26. By means of a voltage-dropping resistor 28, the required more-positive operating potential is applied to the anode 16 and to the focus coil 18.

The target includes a face plate 30, which is at anode potential. Insulatingly supported within a slot in the target is a plurality of wires 32. Each one of these wires is separated from the other by a material such as glass and is mounted so that one end extends through to the outside face of the tube, which is finished in fiat fashion so that a dielectric writing medium 34, such as paper, may be passed extremely close to the wire points which are arrayed in a column, to receive electrostatic charges. An external plane or conductor 36 is connected to the anode and extends along the column of wire points, and is spaced therefrom.

In operation, the cathode-ray beam which emanatesv from the cathode is deflected by the deflection-signal source to sweep across the portions of the wires which are inside the tube. Whether or not a wire is energized is determined by the intensity-control signals received from the signal source 24 at the time the electron beam is directed upon it. Thus, if the deflection signals and the intensity-control signals are being received from a suitable scanning mechanism, such as a facsimile scanner or television camera, and if the writing paper 34 is moved at a synchronized vertical scanning speed, a pattern of charges will be deposited on the writing paper, which when subsequently developed, using well-known electrostatic developing techniques, will produce a visible image of the original copy.

Heretofore, each one of the wires 32 in the target was separated from the adjacent wire by the glass insulating medium within the target. Since the wires are substantially parallel to one another, the wire-to-wire capacity is high and the wire-to-ground capacity is low. Accordingly, when the electron beam strikes a given wire and causes it to charge toward cathode potential, which is necessary before the wire can discharge, to a lesser degree all succeeding wires also charge toward cathode potential because of the coupling capacity between them.

In accordance with this invention, wire-to-wire capacity is minimized by reducing the parallel length of each writing wire to the shortest possible, and also by minimizing the solid dielectric enclosed length of the wire. As may beseen in Figure 2, which is an enlarged cross section of the support 40 for a reading wire in the target shown in Figure 1, each one of the reading wires 32 is supported spaced from each other between two semicylinders 40A, 40B of glass. These semicylinders are sealed together'to support the writing wire with the writing points 42 extending external to the tube. The sides of the semicylinders are sealed at points 41A, 41B by means of a vacuum seal to the outside portion of the face plate 30. An opening 43 is made in the interior portion of the faceplate to permit the electron beam to impinge upon a portion of the writing wire. This portion of the writing wire extends outside of the semicylinders and is attached to a glass rod 44, which itself is'sealed to the glass semicylinder 40B.

It will be appreciated that the view shown in Figure 2 is an end view of the arrangement whereby the writing wires may be mounted. The two semicylindrical halves will be in a slot in the target face plate and will extend over thatportion of the face of the target which it is desiredto use for writing. Each one of the writing wires is mounted spaced apart from the adjacent writing wires. The length of writing wire parallel to an adjacent writing wire is reduced considerably and the amount of solid dielectric between writing wires is also reduced considerably over that which has been used previously.

Figure 3 shows an end View of an arrangement for supporting the writing wires which provides still less solid dielectric between the writing wires and still less length of writin wire parallel to an adjacent writing wire. Effectively, an arcuate sector of dielectric material 46, such as glass, is formed of two abutting arcuate sectors 46A, 463. These have one end of the writing wire 32 sealed between the abutting portions with the terminating end 32A substantially flush with the exterior periphery of the arcuate sector. The other end 3213 of the writing wire is attached to one end of the arcuate sector 46B, so that the writing wire effectively forms a chord with the arcuate sector. The means for fastening the wire end 32B to the arcuate sector end 46B includes a glass rod 44 sealed between the arcuate sector 46B and the face plate 5t) ofthe target. The target face plate is slotted over the writing wires to permit access thereto by the electron beam. The length of the writing Wire required by this embodiment of the invention is made as short as possible, and its dielectric enclosed length is held to a minimum. Thereby, the wire-to-wire capacity is minimized, which reduces the wire-charging and discharging time for a given beam voltage in current.

It will be understood that both in the case of the cylin der shown in Figure 2 and the arcuate sector shown in Figure 3, well-known means are employed for effectively supporting the cylinder and arcuate sector from the face plate so that the face plate is sealed and, accordingly, the tube is also sealed.

There has accordingly been shown and described herein a novel and improved target structure wherein arcuate portions of a hollow cylinder are employed to support the writing wires in an electrostatic writing tube in a minimum of dielectric enclosed length. While in the embodiments of the invention described the configurations employed are those of arcuate portions of a cylinder, it will be understood that this is by way of illustration and should not be construed as a limitation upon the invention, since it will be obvious that other geometric forms may be used without departing from the spirit and scope of this invention.

We claim: I

1. In an electrostatic writing tube of the type having a target including an array of separate writing wires insulatingly supported in the face plate of said tube with one of their ends external to said tube, and having electron bearn means for raising the potential of selected ones of said wires until a discharge occurs to an anode external to said tube, an improved arrangement for supporting each Writing wire comprising two adjacent arcuate portions of a hollow cylinder made of a dielectric material, means for supporting said two arcuate portions of a hollow cylinder to extend externally from said target face plate in an abutting relationship with the portion of each writing wire terminating in said one end extending therebetween, means for holding the end of each writing wire oppositesaid one end to extend a portion of each writing wire across one of said two adjacent arcuate portions of a hollow cylinder, a slot in said target face plate positioned over the portions of said writing wires extending across said one arcuate portion and through which said electron beams can raise the potential of selected ones of said wires.

2. In an electrostatic writing tube of the type having a target including an array of separate writing wires insulatingly supported in the face plate of said tube With one of their ends external to said tube, and having electron beam means for raising the potential of selected ones of said wires until a' discharge occurs to an anode external to said tube, an improved arrangement for supporting each writing wire comprising two halves of a hollow cylinder made of dielectric material, a slot in the side of said target face plate external to said tube, means for holding said two halves of a hollow cylinder in abutting relationship in saidface plate slot with the portion of each Writing wire terminating in said one end being held between said two halves, means for holding the end of said writing wire opposite to said one end to extend the adjacentportion of said writing Wire substantially in the plane of said target face plate, and a slot on the internal side of said target face .plate extending over said portion of said writing wires substantially in the plane of said target face plate through which said electron beams can raise the potential of selected ones of said Wires.

, 3. In an electrostatic writing tube of the type having a target including an array of separate writing wires insulatingly supported in the face plate of said tube With one each writing wire comprising two adjacent sections of the wall of acylinder made of a dielectric material, first means for supporting one of said adjacent sections at one end from the external side of said target face plate, second means for supporting the other of said adjacent sections at one end from the external side of said face plate to abut with its other end the other end of said one of said adjacent sections with the portion of each writing wire terminating in said one end extending between said abutting ends, said second means including means for holding the end of said writing wires opposite to said one end, and a slot in said target face plate positioned over'said writing wires through which said electron beams can raise the potential of selected ones of said wires.

4. In an electrostatic writing tube, an improved target comprising an arcuate sector of a dielectric material, a plurality of separate writing wires having one end extending through said arcuate sector and terminating substantially flush with the external periphery of said arcuate sector, means for fastening the other end of said Writing wires to one side of said arcuate sector, a target face plate means for sealing said arcuate sector ends to said target faceplate, and an opening in said target face plate over said writing wires.

'5. In an electrostatic writing tube, an improved target comprising a hollow dielectric cylinder, a plurality of separate writing wires extending through said hollow dielectric cylinder, separately spaced from oneanother in acommon plane, and with one end substantially flush withthe outer periphery of said cylinder and the other end extending beyond said cylinder, means for fastening said other end of said writing wire to bend the portion of said wire external to said cylinder away from the portion of said wire within said cylinder, at target face plate having internal and external sides, a slot in said target face plate external side to hold a portion of said cylinder,

means to seal said cylinder into said slot with the flush.

ends of said writing wire extending outwardly, and a slot in the internal side of said target face plate opening on No references cited. 

